Monday, November 26, 2007

“It was soon noticed that extraction of a subexpression involved composing the extraction of the address part with cwr and that continuing along the list involved composing the extraction of the decrement part with cwr. Therefore, the compounds car, standing for ``Contents of the Address part of Register number'', and its analogs cdr, cpr, and ctr were defined. The motivation for implementing car and cdr separately was strengthened by the vulgar fact that the IBM 704 had instructions (connected with indexing) that made these operations easy to implement.”

Thursday, November 22, 2007

It is an open secret in the Kingom of Nouns that the King himself has
a half-wit, good-for-nothing brother. His name was expunged from the
official rolls long ago and everyone calls him null.

null is a true oddity in the Kingdom of Nouns. He is a second-class
citizen. This is no doubt due to the fact that he is completely and
utterly incapable of even the most trivial of actions. Whenever he is
asked to perform a task, he responds by taking Exception and throwing a tantrum. Every other citizen in the Kingdom is expected
to at least know his Class and how to present himself to the public. Not null, though.

The residents of the Kingdom take pride in order, so you might imagine
that null's behavior would make him an outcast in the Kindom of Nouns.
In fact, he had been disinherited by every single family in the
kingdom!

null desperately wanted something to do. People would assign him
mundane tasks like standing in for a citizen that was shortly expected
to arrive or standing at the end of a line as a sort of marker.
Occasionally when a request came from the castle, null would return to
deliver the news that no one was able to satisfy the request.

Not everyone was impressed by null's `ability' (so to speak) to take
up space. Sometimes, you just need a member of the right family or
someone that is capable of performing a well-defined task.
Requirements like these were spelled out explicitly in the contracts
that people made: (TaskManager applicant) or (IMowLawns teenager).
But because null was the king's brother, he had a special dispensation
to ignore these restrictions. He'd walk right on in and pretend to be
the manager or the teenager. Of course as soon as you asked him to
do something, like start the mower or even tell you his name, he'd
take Exception and throw another tantrum.

Some people just tried to pretend that null didn't exist and hope that
the king or somebody would catch him as he threw his tantrum. Others
took the time to proofread their contracts and add extra clauses
everywhere to exclude null or deal with him in some ad-hoc way.

Unfortunately, there is no happy ending to this story. null continues
vex and irritate the citizens of the Kingdom of Nouns and no relief is
in sight.

Tuesday, November 20, 2007

Consider this
problem. You are running a high school and you suspect some gang
activities, so you want to be on the lookout for people wearing gang
`uniforms'. But you don't know what any of the uniforms might be.
So you watch the students and take note of what they are wearing:
some have puffy jackets, some have hoodies, some have t-shirts,
some have baggy pants, some have hats that they wear backwards,
etc. etc. etc. Over the course of the day, you see a lot of different
clothing, a lot of different combinations, and all in different colors.
You note, however, that you did see five students wearing purple
puffy jackets, baggy pants, and red baseball caps. What is the
liklihood that this is a gang uniform?
Obviously, it will depend on the size of the student population and
the prevalence of certain kinds of clothing, but in the extreme case
where you see, say, fifteen students with the *exact* same outfits
that match in twenty-seven different random qualities, you can be
pretty sure that is a gang. On the other hand, if you see two students
that happen to wear the same color puffy jacket and otherwise have
nothing in common, you can write that one off as coincidence.
So given the number of students and the relative prevalence of various
clothing elements, how many points of coincidence do you need to
be fairly certain you have found a gang uniform?